1. Field of the Invention
This invention relates to improvements in the recovery of hydrogen chloride from gaseous product streams containing chlorinated hydrocarbons such as chloromethanes.
2. Summary of the Prior Art
Hydrogen chloride as a gas and in aqueous solution as hydrochloric acid are commercially valuable products which may have a variety of uses including the production of chlorinated organics, e.g., hydrochlorination of methanol to form methyl chloride, and other chlorination, polymerization, isomerization, alkylation and nitration reactions; production of food products, e.g., corn syrup and sodium glutamate; in the metals industry, e.g., pickling and metal cleaning; in the petroleum industry, e.g., acidizing of formations; and other miscellaneous end uses such as industrial cleaning of equipment.
Hydrogen chloride and hydrochloric acid may be produced by several different routes, including as a by-product in organic syntheses such as the thermal chlorination of methyl chloride to form more highly chlorinated methanes, e.g., methylene chloride, chloroform and carbon tetrachloride. The organic syntheses route, however, results in a substantially dry gaseous stream containing hydrogen chloride and organics, and common practice is to separate the hydrogen chloride from the organics by partially condensing the gaseous stream at essentially atmospheric pressures, which commonly requires large amounts of refrigeration involving the use of liquefied gases such as liquid ethylene at low temperatures, for example, of from -50.degree. to -85.degree. C.
The need to use such low temperature refrigeration necessarily entails correspondingly high energy consumption. Further, the use of such low temperature refrigeration may necessitate "defrosting," insofar as ice and frozen hydrogen chloride hydrates accumulate on the equipment which interferes with its normal operation and which may also cause increased corrosion problems due to accumulation of such ice along with some hydrogen chloride. Such "defrosting" operations typically entail a complete shutdown of the condenser equipment and removal of frozen material from the unit, and may also lead to certain losses in product yields.